Sinapis alba is an annual herb to 70 cm tall, rough-hairy.
Leaves alternate, lower leaves to 20 cm long, deeply pinnately divided, leaflets toothed, stalked, widest above middle, leaves smaller upwards and less divided, becoming stalkless.
Flowers yellow, 1.5 cm wide, 4-parted; blooming June-Aug.
Fruit dry, capsules 2-parted, to 1.5 cm long, bristly-hairy, each side 3-veined, constricted between seeds, beak to 2 cm long, flat, often curved, tip pointed, seeds, 4-8, 0.2 cm long.
Wetland status: UPL.
Frequency in NYC: Very infrequent.
Habitat: Open soil, roadsides. Sometimes cultivated for mustard seed or salad greens.